Learn Turkish: Burası bir banka mı?

Bu means "this" and is typically used to point out specific objects or people. Burası specifically means "this place" or "here". Since a bank is a location, we use Burası to ask if this location is a bank.

Where is the word for "is" in this sentence?

There isn't an actual word for "is" here! In Turkish, the present tense "to be" verb for the third person (he, she, it, or this place) is often completely left out. The combination of the subject and the noun is enough to mean "This place is a bank."

Why does the question particle take the form of mı here?

The Turkish yes/no question particle changes to match the last vowel of the word right before it, following a rule called four-way vowel harmony. Because the last vowel in banka is an "a", the particle must take the "ı" form, becoming mı.

Do I have to include the word bir in this sentence?

You do not strictly have to, but it sounds much more natural here. Bir acts as the indefinite article "a" or "an" (as well as the number one). Asking Burası banka mı? would be understood, but using bir is the standard way to identify what a place or object is.